1. Field of the Invention
The present invention relates to a spectrum measuring instrument including a dispersing element and a detector for detecting spectrum light coming out from the dispersing element.
2. Description of Related Art
In spectrophotometry, a dark spectrum without any light irradiation is measured prior to the actual measurement. Thus, a net spectrum is found by subtracting a detection signal of the dark spectrum from a spectrum actually measured by irradiating light to a sample.
However, measuring the dark spectrum alone can only compensate an offset signal of the detector.
During the light irradiation state, light other than the one subject to measurement is also incident on a detecting element under the influence of irregular reflection occurring inside the housing of the spectrum measuring instrument, diffuse-reflection occurring on the surface of the diffraction grating, light in the orders other than the measuring order, etc., which causes a stray light noise that changes the level of the entire signal of a spectrum of transmission light.
In order to remove adverse effects of such unwanted light, the internal of the housing of the spectrum measuring instrument is painted black, a masking slit is provided around the measuring light traveling path, etc. However not all the stray light in the order of 10−3 or less in the intensity ratio can be removed by these methods.
Also, the surface of the detecting element is generally covered with a light transmitting window to protect the element. Hence, regularly reflected light from the surface of the detecting element strikes the inner surface of the light transmitting window, and reaches the detecting element again, thereby deteriorating the measurement accuracy of the spectrum of transmission light. In particular, because the surface of the detecting element has a periodic structure, diffracted light toward one specific direction becomes stronger than the rest. This diffracted light also strikes the inner surface of the light transmitting window, and reaches the detecting element again, thereby deteriorating the measurement accuracy of the spectrum of transmission light.
The present invention, therefore, has an object to provide a spectrum measuring instrument capable of removing adverse effects of unwanted light generated inside the spectrum measuring instrument by processing a detection signal from a detecting element.
The present invention has another object to provide a spectrum measuring instrument capable of removing adverse effects of unwanted light generated by reflection and diffraction occurring on the surface of the detecting element by processing the detection signal.